It is a common practice during warming-up of an internal combustion engine to supply a larger quantity of a rich fuel-air mixture in comparison to normally idling, by closing the choke valve and slightly opening the throttle valve. The choke valve and the throttle valve are maintained closed and opened, respectively, until the temperature of the engine lubrication oil rises. This operation is done either manually or by means of an automatic choke mechanism.
However, explosive after-burning often occurs when an ignition key switch is turned off while warming up the engine with the choke valve closed. It takes some time before the engine stops completely under the effect of its inertia force. During this time, a large quantity of fuel is sucked and exhausted without being combusted. Then the fuel becomes ignited and combusted in the exhaust system of the engine. This is the reason why after-burning occurs.
An object of this invention is, therefore, to provide an apparatus for preventing such after-burning, even if the ignition key switch is turned off, in an internal combustion engine being warmed up, with its choke valve closed and its throttle valve opened to a greater extent than during normal idling.
Another object of this invention is to provide an apparatus for closing the throttle valve when the ignition key switch is turned off during warming-up.
Still another object of this invention is to provide an apparatus for opening the choke valve when the ignition key switch is turned off during warming-up.
This invention has been achieved by taking notice of the fact that the unburnt fuel-air mixture discharged into the exhaust system can be prevented from after-burning by decreasing the quantity of, and, further, lowering the ratio of fuel in the fuel-air mixture sent to the engine after turning off the ignition key switch. This can be attained by taking any of the following three steps on turning off the ignition key switch: (1) returning the throttle valve to an idling position; (2) opening the choke valve; or (3) returning the throttle valve to the idling position and opening the choke valve. Therefore, this invention provides a pressure responsive actuator which is actuated by the negative pressure in the air intake manifold. This pressure responsive actuator actuates the throttle valve and/or choke valve, and thus serves as an element to change the air-fuel ratio or the quantity of the air-fuel mixture supplied to the engine. More concretely, closing the throttle valve and/or opening the choke valve is done forcibly by this means.